This invention relates to a wet-type developing unit used in an electrophotographic apparatus, such as a laser printer, a facsimile, a copy machine, or the like, and in particular, relates to a wet-type developing unit for developing an electrostatic latent image formed on a photoreceptor belt.
A conventional wet-type developing unit comprises a development roller to develop an electrostatic latent image formed on a surface of a photoreceptor belt. That is, the development roller renders the electrostatic latent image visible with a liquid developer to form a visible image pattern on the surface of the photoreceptor belt. A squeeze roller is disposed next to the development roller so that its outer peripheral surface presses the surface of the photoreceptor belt. The squeeze roller rolls the visible image pattern and squeezes or removes excess liquid developer from the surface of the photoreceptor belt. A first backup roller is disposed so as to face the development roller across the photoreceptor belt and to press a back surface of the photoreceptor belt. The first backup roller maintains an even interval between the development roller and the photoreceptor belt. A second backup roller is disposed so as to face the squeeze roller across the photoreceptor belt and to support the photoreceptor belt pressed by the squeeze roller.
In the conventional wet-type developing unit, a solid structure or casing is necessary to press the photoreceptor belt with large pressing power by using the combination of the squeeze roller and the second backup roller. Accordingly, the conventional wet-type developing unit has a problem that it has large size and heavy weight for the strong structure.
Moreover, in the conventional wet-type developing unit, a toner density controller is necessary to deal with consumption of charged particle toners and with decrease of toner density. Accordingly, the conventional wet-type developing unit has a disadvantage that the toner density controller requires a large size for the wet-type developing unit and rises the cost of the wet-type developing unit.
Such a developing unit is disclosed in Japanese Unexamined Patent Publication No. 11-231743.
In the meantime, another conventional wet-type developing unit comprises a development roller. A supplying roller is disposed next to the development roller to supply liquid developer for the development roller. Bias voltage is supplied between the supplying roller and the development roller to increase toner density of the liquid developer adhered on the development roller. A squeeze roller is disposed next to the development roller at a predetermined interval to remove excess liquid developer from the development roller.
Though the conventional wet-type developing unit can change the toner density of the liquid developer adhered on the development roller, it is hard to control the toner density. In addition, both of the supplying roller and the squeeze roller require a large size for the conventional wet-type developing unit.
Such a developing unit is disclosed in Japanese Patent No. 2795395.
It is therefore an object of this invention to provide a wet-type developing unit which can reduce pressing power given to a squeeze roller.
It is another object of this invention to provide a wet-type developing unit which has a small size and is light in weight.
It is still another object of this invention to provide a wet-type developing unit which cm control a toner density of liquid developer adhered on a development roller.
In is still further object of this invention to provide a wet-type developing unit which is inexpensive.
Other object of this invention will become clear as the description proceeds.
According to the aspect of this invention, a wet-type developing unit is for developing by using liquid developer an electrostatic latent image formed on a photoreceptor. The liquid developer includes charged toners. The wet-type developing unit comprises a reservoir for reserving the liquid developer. A development roller has an outer peripheral surface wetted by the liquid developer reserved in the reservoir and forms a liquid developer film on the outer peripheral surface to developing the electrostatic latent image by using the liquid developer film. An electrode member is located at a predetermined distance from the outer peripheral surface and applied with a voltage to reduce thickness of the liquid developer film while moving the charged toner toward the development roller.
According to the another aspect of this invention, an electrophotographic apparatus comprises a wet-type developing unit for developing by using liquid developer an electrostatic latent image formed on a photoreceptor. The liquid developer includes charged toners. The wet-type developing unit includes a reservoir for reserving the liquid developer. A development roller has an outer peripheral surface wetted by the liquid developer reserved in the reservoir and forms a liquid developer film on the outer peripheral surface to developing the electrostatic latent image by using the liquid developer film. An electrode member is located at a predetermined distance from the outer peripheral surface and applied with a voltage to reduce thickness of the liquid developer film while moving the charged toner toward the development roller.